The present invention relates to the technical field of electronic circuits. More particularly, embodiments of the present invention relate to adjustable voltage reference circuits having low temperature drift.
In electronic circuits, a voltage reference is an electronic device that ideally produces a fixed voltage irrespective of operating conditions, such as power supply variations and temperature changes. Voltage references are used in power management integrated circuit chips, analog-to-digital converters and digital-to-analog converters, and other measurement and control systems. The voltage reference often can determine the performance of power management integrated circuit chips. A reference voltage source can be implemented in a wide variety of ways, for example, bandgap reference voltage source, bandgap reference with second-order temperature compensation, Zener-based reference voltage source, and E/D (Enhancement/Depletion) reference voltage source, etc.
FIG. 1 shows an example of a convention E/D NMOS reference voltage circuit, in which a depletion-mode NMOS transistor M1 and an enhancement-mode NMOS transistor M2 are connected in series. The voltage at the common node between M1 and M2 is fed to a source follower depletion-mode NMOS transistor M3. The output voltage is determined by the combination of depletion-mode NMOS transistor M4 and enhancement-mode transistor M5.